Microfacies and depositional environment of Late Cretaceous to Early Paleocene oil shales from Jordan

The purpose of this study is to better understand the depositional setting of Late Cretaceous to Early Paleocene oil shales from southeast and central-east Jordan. One core from both the Jafr and the Azraq-Hamza Basins was logged, and their lithology, texture, and ichnofabrics were recorded. A total of 79 thin sections were analyzed petrographically, and eight microfacies types recognized. Both cores show lithologic and petrographic similarities. The oil shales are Maastrichtian to Danian in age and can be described as organic matter and calcite-rich mudrocks. The most abundant granular components are foraminifera and various types of phosphatic bio- and lithoclasts. Macrofossils (bivalves, ostracods, echinoderms) were recorded in some intervals. The current results were compared with data from a previous publication on Maastrichtian oil shales from the Jafr Basin. A new model explaining the deposition of the oil shales of the Jafr and Azraq-Hamza Basins is proposed. The onset of the Maastrichtian oil shale deposition in both basins coincides with the early Maastrichtian transgression in this region. The organic matter-rich sediments were deposited in a mid to outer ramp setting below the storm wave base. Younger oil shales of Late Maastrichtian to Danian age were deposited in a shallower environment, below the fair weather wave base. The Cretaceous/Paleogene boundary is marked by a hiatus in both cores. The Danian oil shales show relatively lower “total organic carbon” content than the Maastrichtian ones. The former are believed to have been deposited in more oxygenated bottom waters of a mid-ramp zone.